For example, for the detection of the stroke position of a piston rod of a hydraulic cylinder, it is customary to do a computation by converting into pulses the output signals from a magnetic sensor mounted on the cylinder side with a number of magnetic scales equally spaced embedded in the piston rod.
The magnetic sensor is intended to produce sinusoidal waves having one cycle per the minimum distance (one scale span) of the magnetic scale by the stroke of the piston rod, the output sinusoidal waves being set in a pair so as to be 90.degree. out of phase with respect to one another.
Detection of the stroke position of the piston rod is achieved by converting these outputs e.sub.A, e.sub.B from the sensor by the use of a comparator into square waves e.sub.A0, e.sub.B0, then inputting them into a phase discrimination or directional discrimination/multiply circuit, producing forward and backward pulses based on the following formulas, and counting these pulses by means of an up-and-down counter. ##EQU1## Where e.sub.A0 (.uparw.); pulses generated upon rise of e.sub.A0,
e.sub.B0 (.uparw.); pulses generated upon rise of e.sub.B0, PA1 e.sub.A0 (.uparw.); pulses generated upon rise of e.sub.A0, PA1 e.sub.B0 (.uparw.); pulses generated upon rise of e.sub.B0, PA1 e.sub.A0 ; inversion signals of e.sub.A0, PA1 e.sub.B0 ; inversion signals of e.sub.B0, PA1 .multidot.; logic product.
Thus, as for the resolution power of position detection, it is possible to detect a quarter of a cycle of the sensor output, i.e. up to the position of a quarter of a stroke of one scale span of the magnetic scale.
With such a system, however, one cycle only of the sensor output can be divided into four, and so improvement of the detection precision of stroke position requires an arrangement of the respective scale markings of the magnetic scale at short intervals. But, there is a processing limit in making fine magnetic scale marks on the surface of the piston rod, and this does not allow detection of very small strokes, accordingly.
The object of the present invention is to provide a system for processing position signals wherein a highly accurate detection of very small strokes can be made with the magnetic scale having marks at small intervals or pitches.
A further object of the present invention is to provide a system for processing position signals wherein the detection of position can be performed accurately and safely in any area of the output of the sensors.